"Experts say that migrations from Unix to Linux have slowed down because all the low-hanging fruit has now been picked. Linux growth in the U.S. x86 server market has, over the past six quarters, started to falter and reverse its positive course relative to Windows Server and the market as a whole."More here.

Quite frankly, you haven't really used it. I can't speak about Zenworks-for-Linux, which I hear exists, but Zenworks on for netware 5.x/6.x managing Windows clients is simply unbeatable, indispensable and zenworks for servers is no slouch either.

And about groupwise... maybe it's not perfect, but if your network is built around eDirectory it is the best thing going.